1. Field of the Invention
The present invention relates to a signal processing circuit which is used to process a high definition television signal.
2. Description of the Related Art
For adjustment of a dynamic range of a video signal and the like, amplification processing is performed by detecting a reference level of the video signal, and then amplifying the whole signal in accordance with the reference level. For the amplification processing, a method is known in which, as shown in FIGS. 5A and 5B, voltage levels VSYNC1, VSYNC2 (black levels) of a horizontal synchronizing term TSYNC of the video signal are detected, and the amplification processing is performed by use of VSYNC2-VSYNC1 as a reference level VREF.
However, as shown in FIGS. 6A and 6B, the horizontal synchronizing term TSYNC is destroyed in accordance with an input situation or a preprocessing situation of the video signal, and the voltage level VSYNC1 of the term is detected to be higher than a true value. In a case where the reference level VREF calculated from the thus detected voltage level VSYNC1 is used as the reference level of the amplification processing, a gain of an amplifier increases more than necessary, as shown in FIG. 6. As a result, there is a problem that it is not possible to obtain the video signal having a desired output level or dynamic range.